Brief statement of specific research goals for the characterization of the in vitro reactions carried out by the six purified protein of the T4 bacteriophage DNA replication apparatus: a) To figure out the role of nucleotide hydrolysis (ATP) by the 44/62 protein in polymerase movement, and of nucleotide hydrolysis (GTP) by the 41 protein in RNA primer formation. b) To identify and sequence the RNA primer made in vitro, and to map all the sites for RNA primer synthesis on the 0x174, G4 and fd genomes. c) To measure rare replication errors in vitro as a function of varied protein and nucleotide components. This assay is based on the biological infectivity of in vitro synthesized bacteriophage 0x174 DNA virus molecules, quantitating the reversion rate of non-viable mutants with known DNA sequence changes. Depending on the mutant used, we can specifically measure base pair transitions, transversions, deletions or additions.